In computer systems, data is stored in data sets such as files that are assigned a data set identifier such as a file name. In order to uniquely identify a given file, its file name needs to be unique in a given storage space. However, one problem is that files can be assigned file names that are duplicates of other file names. System or application programs are provided for identifying such duplicate file names in a given storage space thus enabling the renaming of the files if appropriate so that their contents or associated data can be subsequently distinguished. However, a problem with such systems is that renaming may not always be appropriate and may have consequential effects. For example, other functionality may be dependent on a file having a particular file name. Changing such a file name may result in the dependent functionality failing to operate correctly.